Patent Application
20080000616
This invention relates generally to the field of heat exchangers, and more particularly to a heat exchanger for use in a personal shower environment which recaptures heat from waste water passing through the shower drain and distributes that heat into the cold water entering the shower to raise the temperature of the cold water and thus reduce the amount of hot water required to maintain a given shower temperature.
This invention relates generally to the field of heat exchangers, and more particularly to a heat exchanger for use in a shower environment which recaptures heat from waste water passing through the shower drain and distributes that heat into the cold water entering the shower to raise the temperature of the cold water and thus reduce the amount of hot water required to maintain a given shower temperature.
It is well known that showering for the purpose of maintaining cleanliness is almost universally practiced in civilized society. There is hardly any form of habitation, whether personal residences, commercial habitations, or miscellaneous bathing facilities, that does not provide the necessary equipment for showering. Showering has become, in modern society, so commonplace that many individuals shower at least once per day. Many prefer showering to bathing because it is ready for use more quickly, cleans more effectively, and may require less hot water if not excessive in duration.
Despite the fact that showers of reasonable length and temperature may consume less hot water than bathing in a tub, the fact remains that a substantial amount of hot water is lost down the drain, since the shower water remains in the shower installation for only a very brief period of time, in which only a small portion of it's heat energy is utilized. This, of course, is wasted energy, and represents an expense in fuel or electricity to heat the water which could be substantially reduced if some of the unused heat in the waste water could be recaptured and put to use.
Devices for efficiently and economically exchanging heat between two fluids have been well known for many years and are widely used throughout industry. None of these devices, however, would be practical or effective in the application of recovering heat from the waste water passing through the drain conduit of a shower installation because of the unique environment and requirements of such a system, such as not interfering with the free flow of drain water, not being conducive to clogging, being easy to clear in the event of a clog using standard methods, adapting to existing standard plumbing fittings, and fitting into the typically available space. Additionally, this device must meet the applicable plumbing standards & codes in order for it to be legally and widely installed. Further, this device must have an adequate heat recovery efficiency to justify its purchase & installation cost to the consumer. U.S. Pat. No. 5,791,401 discloses a heat recovery device for personal showers, however the designs disclosed therein are expensive to manufacture because of the complex assembly process, and the inefficient use of materials, and the device has a low operating efficiency.
Thus, there is a need for a more practical, less expensive, more efficient, maintenance-free, and trouble-free device for recapturing heat from shower waste water after it has entered the shower drain and transferring it to the incoming cold water before the cold water is mixed with the hot water and enters the shower head.
The present invention substantially if not entirely meets all of the previously mentioned requirements for a heat recovery device intended for use in the environment of personal shower installations.
Thus, in its broader aspects, the present invention is a heat recovery device adapted for use in the drain conduit of standard shower installations having a hot water supply line, a cold water supply line, a means for mixing water from both lines to deliver water at a suitable temperature to the shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water in the cold water supply line. In this environment, the heat recovery device of the present invention comprises a generally tubular first conduit formed of a material having a high degree of thermal conductivity, this conduit having an inlet that is connected to and in close proximity to the shower drain so that waste water entering the drain will pass into the conduit inlet end, and the exit end of the first conduit connected to the waste water plumbing to receive the water exiting the first conduit. A second conduit means is connected in series with the cold water supply line and is thermally operatively associated with the first conduit in such a way as to transfer the thermal energy from the warm drain water passing through the first conduit to the cold supply water passing through the second conduit and thus raising the temperature of the cold supply water before it reaches the mixing means.
In a more limited aspect, the area between the inlet and outlet ends of the first conduit are disposed at a lower level than the ends, so that conduit remains substantially filled with water at all times and functions as a water trap. Preferably, the central portion of the first conduit lies in a plane that is disposed at an angle to the vertical plane that the inlet and outlet ends of the first conduit lie in, and most preferably, the central area of the first conduit lies in a substantially horizontal plane.
The heat recovery device comprises a second conduit formed of a material having a relatively high degree of thermal conductivity, and being disposed in an intimate heat exchange relationship with the first conduit, and having an inlet end connected to the upstream portion of the cold water supply line, and a downstream portion connected to the mixing valve, so that cold water passing through the second conduit receives thermal energy from the warm waste water passing through the first conduit.
In certain embodiments, the first conduit is formed with helical convolutions in the outer surface, such that the external surface of these convolutions, when combined with a surrounding smooth tubular member, will form the second conduit means, thus placing the two conduit means in intimate thermal contact with each other. The convolutions in the wall of the first conduit also serve to impart turbulence to the drain water passing therethrough, thus increasing the convective heat transfer from the drain water to the wall of the conduit. The convolutions in the wall of the first conduit also serve to impart a spiraling flow to the drain water passing through, thus increasing the velocity of the flow and therefore increasing the rate of convective heat transfer from the drain water to the wall of the conduit.
In one variation of this embodiment, the spiral convolutions are comprised of a single helical groove.
In another variation of this embodiment, the spiral convolutions are comprised of two or more helical grooves, which are joined near the ends by a partial or complete circular groove in said first conduit. These circular groove features allow the multiple spiral flow paths of the second conduit to be in communication with each other, and thus allow the cold water to flow through all of them in parallel.
In another variation of this embodiment, the multiple spiral convolutions are comprised of two or more helical grooves, but rather than being joined by a circular feature near the ends of the first conduit member, they are joined by circular features near the ends of the outer tubular member. These features allow the multiple spiral flow paths to be in communication with each other, and thus allow the cold water to flow through them in parallel. Having this feature on the outer tubular member, instead of the first (inner) conduit member, has the benefit of removing the interruption to the inner helical flow path that this feature creates in the first conduit. Therefore, the inner helical flow will be more robust with this configuration, and have improved convective efficiency.
In another variation of this embodiment, the spiral convolutions are asymmetrical in cross section, such that the flow in the first conduit will encounter steeper oblique obstructions along the outer walls as it goes forward through the conduit, thus imparting more rotational energy to the flow stream, and more effectively increasing the velocity of the flow and convective efficiency. The asymmetry of the helical feature provides a smooth transition on the downstream side of the feature, thus encouraging the flow to remain attached to the surface, and causing the next steep oblique surface to be more effective in promoting the helical flow pattern favoring convective efficiency.
I another variation of this embodiment, the outer wall of the first conduit is made up of two layers of material. This feature allows the second conduit to use the outer layer of the first conduit as its functional inner surface, so that the first and second conduit do not share a common wall. This is an important and required safety feature (for example in U.S. plumbing installations carrying drinking water), which is designed to prevent a leak in any one conduit wall from flowing into the other conduit. Preferably, a narrow gap is present between the two layers of the first conduit wall, so that a leak from either conduit mean will have a path to the outside and therefore be detectable. For example, to ensure formation of said narrow gap during the manufacturing process, a fibrous material that can withstand the high temperatures and stresses of the manufacturing processes may be placed between the two layers of the first conduit wall prior to the forming process, so that a leak from either conduit mean will have a path to the outside and therefore be detectable.
In one embodiment of this invention, the single, helically convoluted first conduit which extends substantially in the horizontal plane and has ends that bend upward at approximately 90 degrees to the vertical plane, combined with the relatively smooth outer tube over the convoluted area forming the second conduit means, is substantially straight.
In another embodiment, the convoluted, horizontally positioned part of the first conduit means is curved approximately 180 or more degrees while remaining in the substantially horizontal plane, thus locating the ends relatively close to each other, more closely representing the configuration of a conventional drain trap. An exemplary drawing of this embodiment is shown in
In another embodiment, two separate sections of the first conduit are joined with an approximately 180-degree conduit section, thus disposing the two sections in a substantially parallel position to each other. The two respective second conduits are connected by a connector conduit that provides for a flow path from one second conduit means to the other.
In yet another embodiment, three, four or more sections of the first conduit are joined with suitably angled conduit sections, elbows or fittings, and the corresponding second conduit sections are brought in fluid communication by two, three or more connector conduits.
Having briefly described the general nature of the present invention, it is a principle object thereof to provide a heat recovery device adapted for use in the drain conduit of a shower installation in which heat in waste water passing through a shower drain conduit is recaptured by transferring it to the cold supply water before it enters the mixing valve and is combined with the hot water supply and enters the shower head.
Another object of this invention is to provide a heat recovery device as disclosed which is designed and constructed to replace the standard drain trap present in all shower equipment installations and to function in the same manner as a water trap.
It is another primary object of the present invention to provide a heat recovery device as disclosed which can be easily and economically manufactured and installed in new or existing shower equipment installations and is entirely compatible with industry standard plumbing equipment utilized in such installations.
It is still another object of the present invention to provide a heat recovery device which is situated in a shower equipment installation such that it is in close enough proximity to both the shower drain and the mixing valve so as to minimize the heat lost in the existing conduits.
It is still another object of the present invention to provide a heat recovery device that provides an intimate thermal contact between the drain water of a shower installation and the cold supply water of a shower installation, such that a substantial proportion of the thermal energy in the waste water is recovered by transferring the energy to the cold supply water.
It is still another object of the present invention to provide a heat recovery device that provides a safe separation between the drain water of a shower installation and the cold supply water of a shower installation, such that a failure of either conduit means will not allow contamination from the water in either conduit to enter the other conduit. It is still another object of this invention to provide a heat recovery device that requires a minimum amount of material & labor to manufacture in order to be cost effective relative to the value of the heat energy that it can recover.
It is another object of this invention to provide a design that uses the most highly automated & accurately repeatable manufacturing processes that can be economically employed to produce the product.
It is another objective of this invention to provide a design that has the highest possible efficiency for its size and for the amount of material used in its construction.
The present invention includes a heat recovery device adapted for use in the drain conduit of a shower installation having a hot water supply line, a cold water supply line, a means for mixing water from both said lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water supply before it enters said mixing means, said heat recovery device comprising a section of generally tubular first conduit formed of a material having a relatively high degree of heat conductivity, said first conduit having an inlet end connected to an upstream portion of said drain conduit and an outlet end connected to a downstream portion of said drain conduit so that waste water passing through said drain conduit also passes through said first conduit, said inlet and outlet ends of said first conduit being connected to said upstream and downstream portions respectively of said drain conduit in such a manner that said first conduit between said inlet and outlet ends is disposed at a lower level than said inlet and outlet ends so that said first conduit remains filled with water at all times and functions as a water trap, and contains at least one helical convolution formed in the wall of said first conduit, said heat recovery device further comprising conduit means connected into said cold water line of said shower equipment and being thermally operatively associated with said first conduit such that cold water passes through said conduit means while passing through said cold water line to be exposed to heat from said first conduit from waste water passing therethrough, said conduit means comprising a second conduit formed of a material having a relatively high degree of heat conductivity, said second conduit being disposed in intimate heat exchange relationship with said first conduit, said second conduit having an inlet end connected to an upstream portion of said cold water line and an outlet end connected to a downstream portion of said cold water line so that cold water passing through said cold water line also passed through said second conduit and receives heat transferred to said first conduit from said waste water, said second conduit having an inner wall that comprises a layer of thermally conductive material that conforms generally to the said helically convoluted outer surface of said first conduit, said second conduit having an outer wall consisting of a substantially tubular member that fits closely to the largest diameter parts of said convoluted inner wall and is suitably joined to it, so that the second conduit is comprised of the helical lumen formed between said outer and said inner walls, said outer wall containing at least one opening at each end of the helical lumen for inlet and exit flow respectively of said cold water supply suitable for adapting to common plumbing fittings, whereby heat from said waste water is conducted through said first conduit means to pre-heat cold water passing through said second conduit means before reaching said mixing means.
In variation of this embodiment, said first conduit means of said heat recovery device is substantially straight and generally horizontal, said inlet and said outlet ends are disposed at substantially 90 degrees to said first conduit means, and disposed substantially vertically.
In a further variation of this embodiment, two assemblies of said first conduits and said conduit means are connected in series using a 180 degree conduit section to join them, and are arranged substantially parallel to each other in the generally horizontal plane, and said inlet end of the upstream section and the exit ends of the downstream section of the first conduit sections are disposed in a substantially vertical plane, so that they are parallel to each other and in close proximity to each other.
In yet a further variation of this embodiment, said first conduit forms a loop in the generally horizontal plane, or at a small angle to the horizontal plane, said inlet and outlet ends disposed in relative close proximity to each other, said inlet and said outlet ends disposed at substantially 90 degrees to said first conduit means, said inlet and outlet ends disposed substantially vertically.
In certain embodiments, a spacer material is located between the outer surface of the first conduit and the outer surface of the inner wall of the second conduit. In other embodiments, the outer surface of the first conduit and/or the outer surface of the inner wall of the second conduit is grooved or textured. The spacer material may be, for example, high temperature fibrous material, metal mesh, metal wire, glass fibers, carbon fibers, aramid fibers, or ceramic fibers.
The present invention also includes heat exchanger for transferring heat between a first liquid and a second liquid, comprising a section of generally tubular first conduit for conducting a first liquid, having at least one helical convolution formed in its wall; and a second conduit being thermally operatively associated with said first conduit, said second conduit being disposed in intimate heat exchange relationship with said first conduit, said second conduit having a convoluted inner wall that comprises a layer of thermally conductive material that conforms generally to the outer surface of said helically convoluted first conduit, said second conduit having an outer wall consisting of a substantially tubular member that fits closely to the largest diameter parts of said convoluted inner wall and is suitably joined to it, so that the second conduit is comprised of the helical lumen formed between said outer and said inner walls, said outer wall containing at least one opening at each end of the helical lumen for inlet and exit flow of the second liquid, respectively.
In some embodiments, the heat exchanger of the invention further comprises a spacer material, which is located between the outer surface of the first conduit and the outer surface of the inner wall of the second conduit. In certain embodiments, the spacer material may be metal mesh, metal wire, glass fibers, carbon fibers, aramid fibers, or ceramic fibers. In other embodiments, the outer surface of the first conduit and/or the outer surface of the inner wall of the second conduit is grooved or textured. In these and other embodiments, a space is located between the outer surface of the wall of the first conduit and the outer surface of the inner wall of the second conduit, said space being in gaseous or liquid communication with the surrounding environment, and said space providing a means for accidental leakage of the first or second liquid to escape.
In preferred embodiments, the first and second conduits of the heat exchanger are formed of a material having a relatively high degree of heat conductivity.
In some embodiments of the invention, the inner diameter of the first conduit may be between about 0.5 and about 8 inches, between about 1 and about 6 inches, between about 1.5 and about 2 inches, between about 2 and about 3 inches, between about 3 and about 4 inches, or larger than about 8 inches.
In some embodiments of the invention, the inner diameter of the second conduit is about 25 to about 50%, about 15 to about 25%, or about 5 to about 15% of the diameter of the inner diameter of the first conduit.
In some embodiments of the invention, the pitch of the helical convolutions is about 0.2 to about 12 inches, about 1 to about 8 inches, about 3 to about 6 inches, about 2 to about 3 inches, about 1.2 to about 3.5 inches, or about 1 to about 2 inches.
In some embodiments of the invention, the first conduit has two, three, four or more helical convolutions.
In certain embodiments of the invention, the heat exchanger of the invention is adapted for use in a heat recovery device for use in a personal shower installation, wherein waste water from the shower installation passes through the first conduit, and cold water supply passes through the second conduit.
In other embodiments, the invention includes a heat recovery device adapted for use in the drain conduit of a shower installation having a hot water supply line, a cold water supply line, a means for mixing water from both said lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water supply before the cold water supply enters said mixing means, said heat recovery device comprising the heat exchanger of the invention, wherein waste water from the shower installation passes through the first conduit, and cold water supply passes through the second conduit.
In some embodiments, a hydroforming process is used to simultaneously form the first conduit and the additional layer of material over said first conduit which forms the inner wall of the second conduit.
An improved heat recovery device is disclosed which is adapted for use in the drain conduit of standard shower installations having a hot water supply line, a cold water supply line, a means for mixing water from both lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing through the shower installation, the heat recovery device transferring heat from the waste water to the cold water flowing through the cold water supply line, thus reducing the amount of hot water required for a shower of a given temperature & duration. The heat recovery device consists of a three-layer structure that has a first inner conduit connected into the drain conduit of the shower installation, and an integrally formed second outer conduit connected into the cold water supply line leading to the mixing means and then to the shower head, and in intimate thermal contact with the first conduit. The integrally formed second conduit comprises of a second layer of material to provide a safe separation between the two flow streams, which generally follows the surface of the first conduit and is in close thermal contact with the first conduit. The outer wall of the second conduit is formed by a third layer, which may be a substantially straight tubular structure that is brazed or otherwise joined to the outermost surface of the second layer. The first conduit functions as a drain-trap, and is substantially unobstructed to prevent clogging, and the second conduit guides the cold water helically around the outer perimeter of the first conduit to provide the maximum possible thermal energy transfer between the conduits. The first conduit also contains said helical features in the wall that maximize the convective heat transfer from the drain water by increasing the flow velocity and turbulence of the drain water.
In one embodiment, the heat recovery device of the invention is used to preheat the incoming cold supply water, which reduces the amount of hot water required for a given shower temperature and thus reduce energy usage. It has been estimated that approximately $360 per year could be saved by the average homeowner with electric hot water with a family of four who all shower daily if the heat recovery device of this invention were utilized. The savings for gas or oil hot water would be about $120 per year. By multiplying these amounts by the number of shower installations in the United States alone, one can appreciate the significance of the economic and environmental impact of the present invention.
The novel design disclosed herein provides substantial advantages in manufacturability, material usage, operating and efficiency, which leads to critical improvements in the cost-effectiveness and thus marketability of this device.
Referring to
Referring to
The cold water enters the heat recovery device through a fitting 32 at the end nearest the waste water exit 34, and travels through the device in the opposite direction as the waste water. A cross-over tube 41 is located at the opposite end of the straight sections with respect to the input fitting 32 and the exit fitting 31. The cross-over tube allows the cold water flow to travel from one straight section 40 to the other straight section 39. The warmed cold water flow exits the heat recovery device through fitting 31.
The path of the cold water through the heat recovery device is readily understood from the sectional perspective
The first conduit, particularly represented by 40 in
The devices of the invention will advantageously be manufactured from materials of high heat conductivity. Preferably, such materials are metals. Where the heat exchanger of the present invention is to be used in a shower drain or other plumbing fixture, it will preferably made from copper, a copper alloy, or copper-plated aluminum. Notwithstanding the general preference for metals, some parts of the devices of the invention may be made from other suitable materials, even if they have a low heat conductivity. For example, one or more fittings (elbows & u-turns) or other parts may be made of plastic (e.g. PVC or ABS) although performance will be slightly better with metal fittings since these will create additional heat convection surfaces and conduction areas. In any event, the conduits should be manufactured from materials able to withstand the chemical and temperature properties of the liquids they are designed to carry. It is also contemplated that the inner surfaces of the conduits are coated (for example galvanized) with material suitably chosen to withstand the chemical and temperature properties of the liquids.
Since standard residential shower drains are between 1.5 and 2 inches in diameter, the diameter of the first conduit of the heat exchanger of the invention should preferably be between 1.5 and 2 inches. For other heat exchange applications, such as industrial process heat recovery, the diameter of the first conduit can be any suitable diameter (for example, between about 0.5 and about 8 inches, between about 1 and about 6 inches, between about 1.5 and about 2 inches, between about 2 and about 3 inches, between about 3 and about 4 inches, or larger than about 8 inches.).
Since the wall of the first conduit is convoluted, it has a variable diameter, with a minor inner diameter at its narrowest parts and a major inner diameter at its widest parts. In various embodiments, the major inner diameter is about 25 to about 50% larger, or about 15 to about 25% larger than the minor inner diameter.
The pitch of the helical convolutions of the first conduit may range from about 0.2 to about 12 inches, about 1 to about 8 inches, about 3 to about 6 inches, about 2 to about 3 inches, about 1.2 to about 3.5 inches, or about 1 to about 2 inches.
Several considerations are to be contemplated when choosing the helical pitch of the wall of the first conduit of the heat exchanger of the present invention. A lower pitch distance will result in more. “wraps” of the second conduit around the first conduit, resulting in a longer second conduit and thus a larger area for heat transfer. However, if the pitch is too small, the flow inside the first conduit will not rotate optimally, reducing the convection rate in the first conduit. Furthermore, a longer second conduit may will result in reduced pressure, which may not be desirable. On the other hand, a larger pitch will result in fewer wraps, and a shorter second conduit. This may be remedied at least in part by introducing double, triple, or more helical convolutions (i.e. creating two or more parallel flow paths in the second conduit).
A heat exchanger of the general design depicted in
The measured temperature of the hot water supply was 125 F, and the measured temperature of the cold water supply entering the heat exchanger was 42 F. The mixing valve of the personal shower device was adjusted such that the measured temperature of the water exiting the showerhead was 105 F. The measured temperature of the drain water, as it entered the drain, was 100 F. The drain (i.e. waste) water flowed at approximately 2 gallons per minute, while the cold water flow rate was 0.75 gallons per minute. The cold water and drain water flowed through the heat exchanger in opposite directions. The measured temperature of the cold water exiting the heat exchanger was 72 F (as compared to 42 F when entering the heat exchanger, see above). Thus, the calculated heat exchanger effectiveness for heating cold water was 52%.
Based on this measured temperature increase in the cold supply water from 42 F to 72 F, it was calculated that the percentage of hot water used to achieve a 105 F temperature at the shower head was reduced from 76% (without the heat recovery device) to 62% (with the heat recovery device), resulting in an 18% reduction in the volume of hot water consumed.
For the purpose of comparison to the above described working example, it was calculated that in order to achieve a heat exchanger effectiveness of approximately 50% with a conventional straight-walled (i.e. non-convoluted) design, the heat exchanger would have to be approximately 4 meters long (compare to 0.92 meter length of the device tested in the present Example. Thus, the heat exchanger device and heat recovery device of the present invention represents a very significant improvement over previously known heat exchangers suitable for this purpose, while reducing the installed size of the device in the drain area of a tub or shower, reducing the cost of the device, and greatly shortening the pay back period (amortization) of the device.
While the invention has been described in conjunction with the above working example, it will be understood that it is not intended to limit the invention to such embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/815,773, filed Jun. 22, 2006, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60815773 | Jun 2006 | US |
